Capitalize First Letter

Transform a sentence so that the first letter of each word is uppercase and the rest lowercase.

string capitalization title python-basics

Write a function `capitalize_first_letter(s: str) -> str` that takes a string `s` and returns a new string where the first letter of each word is uppercase and all other letters are lowercase. A word is defined as any sequence of non-space characters (spaces and punctuation are preserved as-is). The input string may contain leading/trailing spaces and multiple consecutive spaces. The function should work for any non-empty string, but may also be called with an empty string, in which case it returns an empty string.

Implement the function exactly as specified.

Constraints

- `0 <= len(s) <= 10^5`
- Input consists of printable ASCII characters.

Example

```python
>>> capitalize_first_letter("hello world")
'Hello World'
>>> capitalize_first_letter("heLLo WoRLD")
'Hello World'
>>> capitalize_first_letter("  hello   world  ")
'  Hello   World  '
>>> capitalize_first_letter("")
''
```

8 points ~10 min

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Hints

Use `str.split(' ')` to split on spaces, but be careful to preserve the original spacing.

A straightforward way is to iterate through the string and track whether you are at the start of a word.

Remember to handle the empty string case explicitly.

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